﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Dema
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("请输入圆的半径");
            double a =double.Parse( Console.ReadLine());

            double s = a * a * 3.14;


            Console.WriteLine("圆的面积是"+s);
            Console.ReadKey();

        }
    }
}
